Hello, so I think one of my g35's cats is going bad. the exhaust makes this weird noise I'm not sure if its a misfire but its sounds weird. when the sound occurs my check engine light flashes on and off. If I need to change my cat what are my options and price range. I heard I can get test pipes I'm not sure. If I get test pipes will it pass smog. Honestly, I need your guy's opinion if one of your cats go bad what would you do?